The present invention relates to a heating resistor type air flow-meter and an engine control system using said heating resistor type air flow-meter, and more particularly relates to a heating resistor type air flow-meter of ratio-metric output type and the engine control system using said heating resistor type air flow-meter.
An output signal from a heating resistor type air flow-meter is transmitted to an engine control unit (hereinafter referred to as "ECU") and converted to a digital signal by an AD converter (hereinafter referred to as "ADC") in the ECU, and then an air flow rate is calculated. If voltage of an electric power source of the ADC at that time, an error is caused in the digital signal after converted. There is a method of reducing the error where a reference voltage in the ECU is input to the heating resistor air flow-meter as an external reference voltage, and the air flow rate signal is proportionally adjusted corresponding to the external reference voltage using a ratio-metric circuit inside the flow meter. The technology is disclosed, for example, in Japanese Patent Application Laid-Open No. 2-85724 (1990).
However, in the above conventional technology, the ratio-metric function is simply added to the heating resistor air flow-meter, and improvement of accuracy in the ratio-metric function is not considered.